It is known to treat an elongated web in a liquid bath by forming the web into a horizontally extending helix having a horizontal succession of turns each partially submerged in the liquid bath and rotating the helix generally about its longitudinal axis to pass all of each of the turns through the bath. The turns of the helix are kept apart by means of a plurality of guide elements equispaced along the vessel containing the bath.
The helix is generally rotated about its longitudinal axis by means of a plurality of driven longitudinally extending rollers arranged above the bath so as to support the turns. Within the bath the web tends to fold over and bunch up on itself so that in reality the greater portion of the web lies under the surface of the bath.
Such arrangements are advantageous in that they provide a relatively complete treatment of the web with the liquid, as is for example necessary in dyeing operations. However, the several driven rollers above the liquid bath exert considerable tensional forces on the web, frequently causing it to break. Such breakdowns necessitate time-consuming and expensive clearing operations which decrease output efficiency.
Another disadvantage axis. such devices is that a relatively long treatment time is necessary, even though much of the workpiece lies under the surface of the bath. Yet another disadvantage is that the bath is difficult to maintain at an even temperature as is necessary for uniform treatment.